1. Field of Invention
This invention is a combination of two safety devices for motor vehicles equipped with air powered brakes. Specifically, an automatic brake adjuster to compensate for wear and a visual dashboard display of brake operation and range of adjustment.
2. Description of the Prior Art
The proper operation and adjustment of brakes on motor vehicles is critical to vehicle safety. Brakes must be periodically checked and adjusted on vehicles to compensate for wear. Adjustment is only one of the safety factors addressed with this automatic slack adjuster or automatic adjustment conversion unit. This device includes a method to monitor brake operation and adjustment using a visual dashboard display. The automatic slack adjuster and the automatic slack adjuster conversion unit both adjust the brake and at the same time monitor operation of the brake and automatic slack adjuster. Position detectors incorporated in the automatic slack adjuster and automatic slack adjuster conversion unit monitor movement of brake components and provide position information to visual indicators. Groups of visual indicators corresponding to each brake location on the vehicle create a dashboard display allowing the driver to monitor operation and adjustment of all brakes on his vehicle. A brake that is not operating or out of adjustment can cause a vehicle to swerve into the next lane or into oncoming traffic. If the trailer brakes are not operating or are improperly adjusted they can cause a truck and trailer to jackknife. In a properly operating air brake system, when the driver steps on the brake pedal, air is directed to the air brake chambers, energizing the air chambers to extend their push rods which are connected to slack adjusters.
The slack adjusters then rotate the S cam or disc brake mechanism which, if properly adjusted, forces the brake shoes/pads against the drums/rotors providing the friction necessary to stop the vehicle. A variety of factors such as a disconnected air line, broken air connection, pinched air line, shutoff air valve to the trailer, non-functioning air relay valve, push rod to slack adjuster clevis pin missing, S cam arm broken, self-adjusting slack adjuster failure and excessive air chamber push rod travel can cause the air brakes to have reduced effectiveness, or become non-operational and dangerous without the driver's knowledge.
Federal Department of Transportation regulations require that all drivers of commercial vehicles perform a pretrip vehicle inspection to include the proper operation and adjustment of all brakes on his vehicle. Using this invention, the driver without assistance, is able to check brake operation and adjustment, the releasing of all brakes, the proper connection of all air lines, the opening of all air valves to the trailers, the timing between the truck and trailer brakes, and other critical safety items. By using this system for the pretrip inspection the driver is provided with increased information, some of which could only be determined in a major truck repair facility. The use of the described device will assure that the brakes are operating to the maximum design efficiency. If any malfunction of the brakes during the operation of the vehicle the driver is informed the first time he applies the brakes.
When brakes are operational, but needing adjustment, that adjustment would be performed by this described device. If, for any reason, the adjustment is not performed, the driver is informed by the visual indicators of the dashboard display which brake location needs manual adjustment or repair to continue safe and legal operation. Vehicles not equipped with the automatic slack adjusters with operation and adjustment monitor can have brake component failure which can cause brakes to become illegal and unsafe without any indication to the driver. Use of the automatic slack adjuster with operation and adjustment monitor alerts the driver to the fact that the air chamber push rod travel has exceeded the legal travel length by the audible alarm mounted in the vehicle's cab and a visual indication at the corresponding brake location on the dashboard display. The visual indicators that make up the dashboard display warn the driver that the brakes are remaining engaged after the driver has released the brake pedal. This condition is usually due to a malfunction or lack of maintenance to the brake system. Anytime a brake remains on, it continues to produce friction and heat, which can be a dangerous situation, possibly causing a brake fire which can spread to the tires and ultimately to the vehicle. This automatic slack adjuster or the manual adjuster conversion unit not only adjusts the brake when needed, it allows the driver to continuously monitor the status of each brake on his vehicle, each time the brakes are applied or released.
The visual indicators which make up the dashboard display allows the driver to easily monitor that all brakes on the vehicle are operating in unison when the brake pedal is applied. The automatic slack adjuster or automatic slack adjuster conversion unit uses an electromagnetic or pneumatic motor to provide the power to compensate for wear of the brake shoes. This arrangement reduces the constant movement of the adjustment mechanism, and the requirement for frequent lubrication of these moving parts. Many of the automatic slack adjusters on the market use the angle of air chamber push rod to slack adjuster as the adjustment control. If the automatic slack adjuster is improperly installed, it will not adjust the brakes properly.
Previous patents for brake monitoring systems have informed the driver or maintenance personnel that the brakes need to be adjusted. Not one previous patent has controlled the adjustment of the brakes and monitored brake operation and adjustment at the same time. All previous monitoring system patents have ignored the critical safety problem of non-operational air brakes on vehicles. Some of the previous patents have marginal accuracy in their measurement of the travel of the brake components, others use a process that can initialize the measuring system so as to invalidate the subsequent measurement of brake adjustment. The aforementioned problems of inaccuracy would provide unreliable or false information to the driver.
Relevant Prior Art U.S. Pat. No. 2,554,065 issued to Shields, May 22, 1951, for a Pneumatically Actuated Brake Slack Adjuster requires disassembly of the air chamber to install an air control valve. The device uses an air piston to provide it's power, which requires more maintenance than air diaphragms, the air valve has a vent to release the compressed air after the adjustment operation is completed, which is an unneeded extra part, inasmuch as the brake chamber is vented when the brake application is completed. This device requires the replacement of the manual slack adjuster, instead of converting the existing manual slack adjuster. Shields did not consider the possibility of broken or missing brake components. Brake component failure would actuate the adjustment control valve on every application of the brakes, possibly adjusting the brake shoes until they are in continuous contact with the brake drum. Last but not least this automatic slack adjuster does not have a means to monitor and display to the driver of the vehicle the operation or adjustment of the brake to which it is attached.
Relevant Prior Art U.S. Pat. Nos. 4,855,712 issued to Wiley, Jr. et al, Aug. 8, 1989, 4,800,991 issued to Miller, Jan. 13, 1989, 4,749,063 issued to Garrett et al., Jun. 7, 1988, 4,642,603 issued to Martinez, Jr., Feb. 10, 1987, and 3,776,329 issued to Hope et al., Dec. 4, 1973, and in the preferred embodiment of U.S. Pat. Nos. 4,757,300 issued to Sebalos on Jul. 12, 1988, 4,583,071 issued to Sebalos et al, on Apr. 15, 1986, and 4,937,554 issued to Herman, Jun. 26, 1990 only inform the operator that the brake needs to be adjusted or is out of adjustment to a point that it has reached an unsafe adjustment condition. A second major failing with the listed patents is that none have a method to indicate if brakes are operational. If a brake is non-operational none of these monitoring systems provide an indication that the brake system has failed. Inasmuch as the above listed patents do not monitor the operation of the brakes, a failure in their adjustment monitoring system would not be detected until scheduled maintenance occurred.
A modified form of U.S. Pat. Nos. 4,757,300 issued to Sebalos (1988) and 4,583,071 issued to Sebalos et al, (1986) indicate a method of monitoring movement of the air brake push rod using a rheostat and voltmeter, but this type of system would show different readings as the voltage in the vehicle's electrical system changed. Any of the following conditions would cause this type of system to give inaccurate information as to the brake adjustment: a battery in a low state of charge, a high electrical demand, a short in the electrical system, dirty or corroded battery terminals, dirty or corroded connections between truck and trailer. Furthermore, the physical size of the meters required to display the information for each brake of a multiaxle vehicle would require an excessive amount of dashboard space. The attention required to read a bank of up twelve meters in a moving vehicle would detract from the drivers ability to safely operate the vehicle. U.S. Pat. No. 4,855,712 to Wiley, Jr. et al. (1989) lists an external audible alarm, attached to a vehicle's axle, that would sound to indicate unsafe brake condition being caused by out of adjustment slack adjuster. Problems with audible alarms include: the inability of the operator to hear the alarm, the operator would be required to visually check all of the brakes to find out which one is causing the alarm signal, distracting or confusing other operators unfamiliar with the sounding alarm thinking it is an emergency signal. The patent mentions a backup battery system to preclude the need for power from the vehicle's battery system. A backup battery in case the vehicle's electrical system is not functioning would be useless to a highway vehicle's operation. A highway vehicle that is driven with a non-functioning electrical system is in violation of numerous traffic regulations.
U.S. Pat. Nos. 4,800,991 to Miller (1989), 4,749,063 to Garrett et al. (1988), 4,642,603 to Martinez, Jr. (1987), and in the preferred embodiment of U.S. Pat. Nos. 4,757,300 to Sebalos (1988) and 4,583,071 to Sebalos et al. (1986) requires removal and disassembly of the air chamber, which if not properly performed by trained personnel, can cause serious bodily injury and possible death. This modification to the air chamber requires a significant amount of time, equipment and expense. U.S. Pat. No. 4,749,063 to Garrett et al. (1988) requires extensive modification to the existing brake system which includes multiple air flow measuring devices. Also it requires a cleaner environment than normally associated with trucks and/or heavy equipment. The operation of this system in cold climates requires an absolutely dry air source to prevent moisture from freezing in the system rendering it inoperable.
U.S. Pat. No. 4,800,991 to Miller (1989) is a "plurality of indicators which respond solely to the excess actuator motion when the vehicle brakes are applied to provide a visible indication of such excess motion and the probable need for brake adjustment." Based on Miller's summary, this system provides no intent or means to monitor the operation of the brakes. The patent states that "latching circuitry should be used to keep the indicator on once the limit has been reached." If this circuitry was employed in the device it would then eliminate the device as a means to monitor the retraction of that brake. Once the brake had exceeded it's predetermined distance of actuator travel and the latching circuitry was activated, no further indication of brake movement would be provided to the vehicle operator on that monitored brake. Additionally, Miller states the latching circuitry would guarantee the driver would be able to see the warning light since it would stay on until the driver or maintenance personnel reset the circuitry to shut off the light, precluding the use of an audible alarm. U.S. Pat. No. 4,937,554 issued to Herman (1990) only monitors the need to adjust or illegal/unsafe brake adjustment based on a computer comparison of air pressure versus slack adjuster movement. The monitoring system in this patent does not attempt to adjust the brakes or monitor the operation (application and complete retraction) of the brakes. Although Herman's patent uses a dashboard display the information the driver receives relates only to a need to adjust or unsafe/illegal brake adjustment. Herman mentions the possibility of adding a green light to the dashboard display to indicate the slack adjuster has a movement of less than a determined amount, again versus the amount of air pressure applied to the brakes. The driver of a vehicle equipped with the monitoring system described in Herman's patent would have a false sense of security, even possibly caught in a dangerous situation if the brakes were not operating (engaging) when the driver steps on the pedal. Herman tests for air pressure to the brakes at the manifold, however conditions occurring beyond the manifold are not monitored. Situations preventing the brakes from operating yet not identified to the driver on the dashboard display include: air valves to trailer not turned on when trailer is connected; air hose becoming tangled, pinched, or broken during operation of vehicle; air relay valve not functioning and not directing pressure to trailer brakes. In instances like these, the driver would have no warning of brake failure.
In fact, the computer would display an indication of properly adjusted brakes (a green light) since the CPU is only looking for maximum amount of travel of the slack adjusters for a warning signal, not taking into account that in some cases brakes do not operate when the brake pedal is applied. The lack of operation is not monitored nor is the monitoring of retraction of the brakes after the brake pedal is released, both of the aforementioned conditions are serious and possibly dangerous brake failures. Herman states that when the driver first turns on the ignition the CPU would reset itself, zeroing all slack adjuster measurements to initialize the system. However, when the truck is parked, the spring powered brakes are applied. The spring brakes operate similar to the driver applying the brake, but only on the rear brakes of the tractor and possibly the trailer. If the CPU used this measurement to initialize itself, the monitoring system would be in error inasmuch as the slack adjuster would not be in a retracted (zeroed) position. Herman's system could give the driver an indication of properly adjusted brakes, when in fact, the brakes would not be able to stop the vehicle.